In recent years, regulations are tightened on a biological test and a clinical test conducted for the sake of treatment of human diseases. As an alternative for the biological test and the clinical test, research and development have been extensively made on the collection of live cells from the human blood. The collection of cells is conducted by different kinds of cell collecting devices such as a micro-fluidic device, a CTC (Circulating Tumor Cell) chip, a filter, and so forth.
U.S. Patent Publication No. 2007/0259424A1 discloses a micro-fluidic device. The micro-fluidic device disclosed in this patent document includes a top layer, a bottom layer and a plurality of obstacles. Binding moieties, e.g., antibodies, charged polymers, or molecules coupled with cells are coated on the surfaces of the obstacles. The obstacles include micro-posts extending in a height direction from the surface of the top layer or the bottom layer. A sample, e.g., the blood, is admitted through an inlet of the top layer to flow along channels and is then discharged through an outlet of the top layer. The cells contained in the blood are captured by the binding moieties.